The present invention relates to an arrangement for monitoring a rotational speed sensor. During the operation of internal combustion engines, especially of electronically regulated internal combustion engines, it is necessary to determine a defect of the rotational speed sensor as fast as possible and with highest possible reliability. Arrangements for monitoring a rotational speed sensor are known. It is possible with these arrangements to determine a defect of the rotational speed sensor or the rotational speed transmitter. One of such arrangements is disclosed, for example, in the German document DE-OS 3,145,732. Here the output signal of a rotational speed sensor is compared with an auxiliary signal, and an error of the rotational speed sensor is determined when an auxiliary signal occurs, however no output signal of the rotational speed sensor is recognized. As an auxiliary signal, the battery voltage is utilized among others. An error operation of the rotational speed sensor is recognized when the battery voltage a certain time after the actuation of the starter exceeds a predetermined threshold, however no output signal of the rotational speed sensor is determined.
In the known arrangement there is however the disadvantage that an error operation of the rotational speed sensor cannot be recognized during the starting process.
Moreover, in the case of non-running of the internal combustion engine it cannot be recognized as well since then the vehicle electrical system voltage does not exceed the threshold value.